DE102013226091A1 - Cylinder drum of a hydrostatic axial piston machine with a wear protection layer - Google Patents

Abstract

Disclosed is a cylinder drum of a hydrostatic axial piston machine, wherein in the cylinder drum a plurality of cylinder bores are introduced, in each of which a piston is moved wear-intensive. The cylinder bores of the cylindrical drum are nitrocarburized to minimize wear in the salt bath or in the gas, wherein a thin uniform compound layer with a thickness of 4 to 16 microns and a comparatively thick underlying diffusion layer are provided.

Description

The invention relates to a hydrostatic axial piston machine with a cylindrical drum, which has a sliding surface and thus form a sliding pair with another component.

In axial piston machines, a cylindrical drum rotates relative to a stationary disk-shaped control or distributor plate. In the cylinder drum cylinders (holes) are formed in which piston perform a lifting movement along a stroke direction, which is directed axially to the axis of rotation of the cylinder drum. When Schrägachsbauweise a drive shaft to which the Koben are coupled, employed obliquely to this stroke direction. In swash plate construction is a swash plate, to which the collars are coupled, employed obliquely to this stroke direction. Via the distributor plate, the cylinders are alternately connected to a high-pressure side and a low-pressure side of the machine. For example, the cylinder drum and the pistons guided therein form a sliding pair in the sense of the present document.

From the prior art it is known to nitrocarburize the components of sliding pairs and thus to produce a wear protection layer. In this heat treatment process, the chemical composition of the surface layer is changed, so that the strength is increased and the wear behavior is improved. It is known to nitrocarburize in gas or in a salt bath.

The pamphlets EP 1 122 330 B1 and EP 1 122 331 B1 each disclose a process for nitrocarburizing in gas.

The publication WO / 0142528 A1 discloses a method of nitrocarburizing an injector in the salt bath until a tie layer has reached a thickness of up to 3 microns. Thereafter, the injector is further treated in a gas nitriding process. The aim is to keep the connecting layer thin or to re-form it in gas nitriding.

The object of the invention is to provide a cylinder drum of a hydrostatic axial piston machine, which forms at least one other component - in particular with several pistons - a sliding pair, and their wear protection layer are durable and fail-safe even at high system pressures and resulting high friction forces, so that the entire axial piston machine has a long service life.

This object is achieved by a cylinder drum having the features of patent claim 1.

The claimed cylinder drum is suitable as a component of a hydrostatic axial piston machine and has a wear protection layer. According to the invention, the wear protection layer is produced by nitrocarburizing in a salt bath or by nitrocarburizing in the gas and has a comparatively thin ductile bonding layer whose thickness is e.g. 4 to 16 microns. Thus, the cylinder drum tolerates a higher Hertzian pressure compared to versions with a wear protection layer, which was produced in the conventional nitriding or Nitrocarburierverfahren. The abrasive and adhesive wear protection is retained. Due to the small dimensional changes, higher process reliability is possible with low tolerances.

According to a variant (a), the wear protection layer is produced by nitrocarburizing in a salt bath and the bonding layer has a thickness of 10 to 16 μm.

According to a variant (b), the wear protection layer is made by gas nitrocarburizing and the bonding layer has a thickness of 5 to 12 μm.

According to a variant (c), the wear protection layer is produced by nitrocarburizing in a salt bath, and the bonding layer has a thickness of 4 to 8 μm.

In a first application, the cylinder drum is a bushless swash plate cylinder drum.

In a second application, the cylinder drum is a bent axis cylindrical drum.

It is particularly preferred if the wear protection layer has a comparatively thick diffusion layer. For example, the thickness of the diffusion layer may be at least 50 μm.

When the wear-resistant layer is made by gas nitrocarburizing, for example according to variant b, it is particularly preferred if this has been done in two stages, the first stage having comparatively low treatment temperature and comparatively long treatment time, and the second stage increasing the carbon content of the Having bonding layer by adding carbon donors at a relatively high treatment temperature. This increases the carbon content of the tie layer. The two-stage gas nitrocarburizing allows compared to the prior art reduced dimensional changes of the component and a higher process reliability and higher reliability of the Cylinder drum especially for components with small tolerances.

In this case, a carbon donor can be added already in the first stage.

It is particularly preferred if initially more nitrogen was supplied than in an undersaturated furnace atmosphere. This avoids mottling of the cylinder drum by a uniform layer formation on the entire surface.

It is furthermore particularly preferred if subsequently less nitrogen was supplied than in a supersaturated furnace atmosphere. This will prevent excessive growth of the bonding layer and thus its embrittlement.

An inventive embodiment of a cylinder drum is shown in the drawing. With reference to the figures of this drawing, the invention will now be explained in more detail.

Show it

1 a longitudinal section through the cylinder drum according to the invention and

2 the cylinder drum according to 1 in a view.

1 shows a cylinder drum 1 of the embodiment of the axial piston machine according to the invention in slant axis construction in a sectional view. It has approximately circular cylindrical shape and rotates during operation of the axial piston machine about its longitudinal axis 2 , The cylinder drum 1 is on a front side 4 spherically shaped and is with this front side 4 pressed against a distributor disc. The other front side 6 is facing a flange of a drive shaft, wherein the cylinder drum 1 - In the case of a constant machine - is employed against this flange and - in the case of an adjusting - with different angles relative to this flange can be adjusted.

2 shows a view of the front side 6 the cylinder drum 1 , which is facing the flange or the shaft. At its circumference are evenly distributed several cylinder bores 8th placed over a large part of the length of the cylinder drum 1 extend.

With reference to 1 has every cylinder bore in the area of the spherically shaped end face 4 a through hole 10 over which the cylinder bore 8th during its orbit around the longitudinal axis 2 alternately connected to a high pressure kidney and a low pressure kidney of the distributor disc. In every cylinder bore 8th a piston is guided at its from the cylinder drum 1 side facing away from the flange is hinged, wherein the stroke of the piston in the cylinder bore during common circulation is generated by the oblique position of the flange. Thus each piston forms with the cylinder drum 1 - more precisely with the cylinder bore 8th - a sliding pair.

According to the invention, the cylinder drum 1 according to the 1 and 2 nitrocarburized after their production in a furnace with gas or in a salt bath. Thus, in particular in the area of the lateral surface of the cylinder bore 8th an oxide layer OS, an underlying connection layer VS and an underlying diffusion layer DS produced, which serves as wear protection layer of the cylinder bore 8th serve. In the gas nitrocarburizing variant, the bonding layer VS has a thickness of 5 to 12 μm, while the underlying diffusion layer DS has a thickness of at least 50 μm. In this case, a two-stage process can be used, was treated in the first stage with a comparatively long duration and comparatively low temperature of 500 to 510 ° C. In the second stage, the carbon content of the tie layer (VS) was increased by adding carbon donors at a comparatively high treatment temperature.

Disclosed is a cylinder drum of a hydrostatic axial piston machine, wherein in the cylinder drum a plurality of cylinder bores are introduced, in each of which a piston is moved wear-intensive. The cylinder bores of the cylindrical drum are nitrocarburized to minimize wear in the salt bath or in the gas, wherein a thin uniform compound layer with a thickness of 4 to 16 microns and a comparatively thick underlying diffusion layer are provided.

LIST OF REFERENCE NUMBERS

1

cylinder drum

2

longitudinal axis

4

front

6

front

8th

bore

10

Through Hole

DS

diffusion layer

OS

oxide

VS

link layer

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1122330 B1 [0004]
• EP 1122331 B1 [0004]
• WO 01/42528 A1 [0005]

Claims (10)

Cylinder drum of a hydrostatic axial piston machine having a wear protection layer, characterized in that the wear protection layer is prepared by nitrocarburizing in a salt bath or by gas nitrocarburizing and has a comparatively thin ductile bonding layer (VS).  A cylindrical drum according to claim 1, wherein the bonding layer (VS) has a thickness of 4 to 16 μm.  A cylindrical drum according to claim 1 or 2, wherein the wear-resistant layer is made by nitrocarburizing in a salt bath, and wherein the bonding layer (VS) has a thickness of 10 to 16 μm.  A cylinder barrel according to claim 1 or 2, wherein the wear-resistant layer is made by gas nitrocarburizing, and wherein the bonding layer (VS) has a thickness of 5 to 12 μm.  A cylinder barrel according to claim 1 or 2, wherein the wear-resistant layer is made by nitrocarburizing in a salt bath, and wherein the bonding layer (VS) has a thickness of 4 to 8 μm.  A cylindrical drum according to any one of the preceding claims, which is a bushingless swash plate cylinder drum.  A cylinder barrel according to any one of claims 1 to 5, which is a bent axis cylindrical drum.  Cylinder drum according to one of the preceding claims, wherein the wear protection layer has a comparatively thick diffusion layer (DS).  A cylindrical drum according to claim 8, wherein a thickness of the diffusion layer (DS) is at least 50 μm.  A cylinder barrel according to claim 8 or 9, wherein the wear-resistant layer is made by gas nitrocarburizing in two stages, the first stage having a comparatively low treatment temperature and a comparatively long treatment time, and wherein the second step contributes to increasing the carbon content of the bonding layer (VS) by adding carbon donors having a comparatively high treatment temperature.

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